The invention relates to collimators, and more particularly relates to focussing collimators made up of metal foil. In its most immediate sense, the invention relates to focussing collimators of the Platz-Heinzelmann type.
U.S. Pat. No. 3,943,366 to Platz and Heinzelmann discloses a collimator which is made up of strips of lead foil. The strips are adhesively secured together. The strips are not of uniform thickness; as is stated at column 2, lines 63-64, the thickness of the sections 28 is half that of the sections which immediately adjoin them. This dimensioning creates a honeycomb-type structure in which the total thickness of the septa separating the collimator channels is everywhere generally constant. As used herein, the term "Platz-Heinzelmann-type collimator" means a collimator which is built up from adhered-together strips of material and which has a generally constant septum thickness.
The referenced patent discloses that strips of lead foil are heated (as by an induction coil, see column 1, lines 61-63) and then introduced between two mating gears as shown in FIG. 3. These gears produce corrugated lead foil strips which are later glued together to form the core of a parallel-hole (or nonfocussing) collimator.
The method disclosed in the referenced patent is not suitable for producing focussing collimators (e.g. collimators of the cone-beam, fan-beam, astigmatic and multifocal types). This is because focussing collimators cannot be made up from lead foil strips having a corrugation pattern which remains invarient from one end to the other. It is not practical to cut mating gears so as to produce lead foil strips which, when assembled together, will form collimators of the focussing type.
Focussing collimators made of corrugated lead foil are conventionally stamped to an appropriate shape in a die press. Such a method is unsuitable for manufacturing collimators of the Platz-Heinzelman type. This is because extremely high pressures would be needed to compress the strips to half-thickness at the proper location. Conventional die press equipment is not capable of producing strips of appropriate dimensional precison at the pressures which would be required.
As a result, conventional focussing collimators are not of the Platz-Heinzelmann type and Platz-Heinzelmann-type collimators are not of the focussing type.
It would be advantageous to provide a focussing collimator of the Platz-Heinzelmann type. It would also be advantageous to provide a method for manufacturing focussing collimators of the Platz-Heinzelmann type.
One object of the invention is to produce a focussing collimator of the Platz-Heinzelmann type.
Another object is to provide a method for manufacturing a focussing collimator of the Platz-Heinzelmann type.
Still another object is to provide an improved method for manufacturing Platz-Heinzelmann-type collimators.
Yet another object is, in general, to improve on known collimators and methods by which they are manufactured.
In accordance with the apparatus aspects of the invention, there is provided a focussing collimator of the Platz-Heinzelmann type. In accordance with the method aspects of the invention, strips of material are heated to below the extrusion temperature of the material from which they are made. This permits strips suitable for use in Platz-Heinzelmann-type collimators to be manufactured using only slightly elevated pressures. Advantageously, the material is an alloy containing a preponderance of lead and the strips are coated with a high temperature post-processable mold release agent before they are heated.